1. Field of the Invention
The present invention relates generally to the filed of non-volatile memory technology. More particularly, the present invention relates to a magnetoresistive random access memory (MRAM) element with improved magnetization efficiency, and method for fabricating the same.
2. Description of the Prior Art
As known in the art, magnetoresistive random access memory (MRAM) is a non-volatile computer memory technology. MRAM is six times faster than the current industry-standard memory, dynamic RAM (DRAM). It is almost as fast as static RAM (SRAM) and is much faster and suffers less degradation over time than flash memory. Unlike these technologies, MRAM uses magnetism instead of electrical charges to store data.
In general, the MRAM cells include a data layer and a reference layer. The data layer is composed of a magnetic material and during a write operation the magnetization of the data layer can be switched between two opposing states by an applied magnetic field and thus binary information can be stored. The reference layer usually is composed of a magnetic material in which the magnetization is pinned so that the magnetic field, which is applied to the data layer and in part penetrates the reference layer, is of insufficient strength to switch the magnetization in the reference layer.
MRAM is physically similar to DRAM in makeup, although often does not require a transistor for the write operation. However, the most basic MRAM cell suffers from the half-select problem, which limits cell sizes. To be worth putting into wide production, however, it is generally believed that MRAM will have to move to the 65 nm size of the most advanced memory devices, which will require the use of spin-torque-transfer (STT) technology.
Spin-torque-transfer (STT) or Spin Transfer Switching, uses spin-aligned (“polarized”) electrons to directly torque the domains. Specifically, if the electrons flowing into a layer have to change their spin, this will develop a torque that will be transferred to the nearby layer. This lowers the amount of current needed to write the cells, making it about the same as the read process.
However, the prior art MRAM has several drawbacks. For example, the gap fill process of the reference layer using physical vapor deposition (PVD) methods becomes problematic when the aspect ratio of the gap is greater than 2 for example. Besides, as the cell packing density increases, the interference between neighboring cells is not negligible. Therefore, there is a need in this industry to provide an improved method for fabricating the MRAM devices in order to avoid the aforementioned PVD gap fill problem, as well as an improved MRAM structure that is capable of eliminating interference or coupling between neighboring cells.